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TT13.04 - Memristive Properties of Metal/Manganite Devices: Correlation of Charge-Carrier Transport and Redox-State at the Interface 
April 9, 2015   2:30pm - 2:45pm

Resistance random access memory (RRAM), which utilizes two or more resistive states of a material system for data storage, has attracted considerable attention as a future non-volatile memory concept. A large variety of binary oxides and complex transition metal oxides exhibit different resistance states at opposite polarities of electrical stimulation and could thereby be employed as RRAM. It has become widely accepted that resistive switching in oxides is in most cases connected with a voltage-driven oxygen vacancy movement and a resulting redox process. However, the current knowledge of the microscopic details of the redox-processes is very limited. Besides the n-conducting oxides which mostly exhibit filamentary resistive switching, there exists another class of bipolar resistive switching oxide systems, such as several manganites, for which it was demonstrated that the high and low resistive state currents scale with the electrode area implying that forming and switching take place beneath the whole electrode. We have shown that after electroforming of Ti/Pr0.48Ca0.52MnO3/SrRuO3 thin film devices, the chemical changes at the interface between the Ti electrode and the PCMO layer dominate the resistance of this multilayer stack. The reactive metal electrode forms an oxide layer at the Ti/PCMO interface prior to device operation, and applying a voltage to the stack was shown to increase the thickness of the TiO2 layer at the interface, and to deplete the underlying PCMO of oxygen further. Based on the knowledge of the electroforming mechanism, we present an encompassing view of the field-induced valence change during resistive switching at the Ti/PCMO interface. The chemical changes at the Ti/PCMO interface in four different resistive states are investigated by Hard X-ray Photoelectron Spectroscopy (HAXPES), and correlated to the transport-mechanism of charge-carriers across the multilayer stack for each state. A notable difference between the high and low resistive states can be explained through a convolution of several conduction mechanisms, which is in agreement with the observed chemical changes. [1] F. Borgatti, C. Park, A. Herpers, F. Offi, R. Egoavil, Y. Yamashita, A. Yang, M. Kobata K. Kobayashi, J. Verbeeck, G. Panaccione and R. Dittmann, Nanoscale 5, 3954 (2013) [2] A. Herpers, C. Lenser, C. Park, F. Offi, F. Borgatti, G. Panaccione, S. Menzel, R. Waser and R. Dittmann, Adv. Mat. 26, 2730 (2014)

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